selective precipitation of iron

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Inter Refiner

Well-known member
Joined
Apr 19, 2020
Messages
46
hello friends,

I have an aqua regia solution of platinum, palladium, rhodium and a lot of iron, I want to remove iron from them, so I am wondering if there is any possible compound that would selectively precipitate iron?

thank you
 
In my limited experience, it would seem easier to cement the precious metals out of solution with copper, leaving the iron still in solution. Decant/filter to separate the two. You can then redissolve the PM sponge and proceed to try separation by the method of your choice, and treat the solution as waste (after testing of course).

I could be wrong.

How much of each component is in your solution?

Dave
 
This method works definitely, but the ratio is 10:1 iron to pgm, that is a large amount of iron and cementing would not be the best way to handle about 100 kgs of this material


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Inter Refiner said:
This method works definitely, but the ratio is 10:1 iron to pgm, that is a large amount of iron and cementing would not be the best way to handle about 100 kgs of this material
Click to expand...

Perhaps I don't understand your post. You say "the ratio is 10:1 iron to pgm". To me that means there is 10 times as much iron as there is PGM in your solution. That would seem a good time to cement the 1 part of PGMs and leave the 10 parts of iron in solution till you treat it as waste. Am I misunderstanding what you're dealing with?

Dave
 
[/quote]
Perhaps I don't understand your post. You say "the ratio is 10:1 iron to pgm". To me that means there is 10 times as much iron as there is PGM in your solution. That would seem a good time to cement the 1 part of PGMs and leave the 10 parts of iron in solution till you treat it as waste. Am I misunderstanding what you're dealing with?

Dave[/quote]
No you did not misunderstand, but what I am trying to say is that I have about 100 kilograms of this material a week, and cementing doesn’t look practical for such a large quantity


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Well if it’s just PGMs and iron in solution, why not reduce them with iron shot?
If copper is too expensive, I’d do that.


Not sure I understand what “not practical” means.
 
Lou said:
Please enjoy,

Lou.


https://core.ac.uk/download/pdf/77021587.pdf
Click to expand...

Thanks Lou! That's a great article. I really enjoyed reading that. :)

Göran
 
Several options that will work If you are trying to separate out the pgms from the iron.
Assay the material 1st. Then determine the amount of nitric acid you will need to dissolve the iron and the amount of Pd you have in the material. Use 2-3% excess nitric and water on heat at about 140-160 degrees f stirring till no more reaction and then add an additional 1-2% nitric and leach for another 30 minutes to and hour.
All of your iron and Pd should now be in the nitric solution at a solid 0 ph. This will leave your Pt and Rh as powder in the tailings.
Filter and rinse this powder thoroughly with hot distilled water.
Now on your nitric solution as stated by Lou above use iron shot or turnings to cement out the Pd. Filter and rinse thoroughly with hot distilled water to ensure no nitric is left. Then rinse with a 1-3% water HCL solution to remove any residual iron from your Pd powder.
You now have your Pd by itself and your Pt and Rh separated from the iron ready for final separation and refining working with a much smaller volume of material and no HCL involved until this point.
However, as Lou pointed out if you already have it dissolved in AR solution cement your PGMs with the iron shot. Filter and rinse thoroughly with hot distilled water and then with 1-3%HCL water solution to remove any excess iron and then do your final separation and refining. You will find instructions on properly doing so elsewhere in the forum or sell the Dore PGM powder to a refinery as is.
Another option would be to use HCL and 3% peroxide to dissolve the iron and leave the PGMs behind as mixed Dore or the Pd, Pt, and Rh to be further refined.
Personally I would not dissolve this material in AR to separate the iron from the PGMs. Why use the extra chemicals?
Good luck with it.Ron
 
rhwhite67 said:
Several options that will work If you are trying to separate out the pgms from the iron.
Assay the material 1st. Then determine the amount of nitric acid you will need to dissolve the iron and the amount of Pd you have in the material. Use 2-3% excess nitric and water on heat at about 140-160 degrees f stirring till no more reaction and then add an additional 1-2% nitric and leach for another 30 minutes to and hour.
All of your iron and Pd should now be in the nitric solution at a solid 0 ph. This will leave your Pt and Rh as powder in the tailings.
Filter and rinse this powder thoroughly with hot distilled water.
Now on your nitric solution as stated by Lou above use iron shot or turnings to cement out the Pd. Filter and rinse thoroughly with hot distilled water to ensure no nitric is left. Then rinse with a 1-3% water HCL solution to remove any residual iron from your Pd powder.
You now have your Pd by itself and your Pt and Rh separated from the iron ready for final separation and refining working with a much smaller volume of material and no HCL involved until this point.
However, as Lou pointed out if you already have it dissolved in AR solution cement your PGMs with the iron shot. Filter and rinse thoroughly with hot distilled water and then with 1-3%HCL water solution to remove any excess iron and then do your final separation and refining. You will find instructions on properly doing so elsewhere in the forum or sell the Dore PGM powder to a refinery as is.
Another option would be to use HCL and 3% peroxide to dissolve the iron and leave the PGMs behind as mixed Dore or the Pd, Pt, and Rh to be further refined.
Personally I would not dissolve this material in AR to separate the iron from the PGMs. Why use the extra chemicals?
Good luck with it.Ron
Click to expand...
Any upsides of using Iron in stead of Copper to cement out the PGMs?
 
Might want to look into using ammonium hydroxide as a precipitant around pH 3-3.5 range. Only thoughts is some PMG metals might get pulled out due to absorption with large quantities of iron precipitate.
 
Yggdrasil said:
Any upsides of using Iron in stead of Copper to cement out the PGMs?
Click to expand...
Yes as you already have a massive amount of iron in solution and it will not take much to precipitate the pgms that are there. Plus clean up of the pgm powder with weak hcl / h2o will be very easy with no nitric involved. Also iron reacts faster and is cheap for this situation.
Personally, like I mentioned above I'd target the iron with either nitric or hcl/ 3% h202 and not put the pgms into solution to begin with. Then refine everything working with the much smaller volume of just the pgms to separate and deal with. Much simpler and easier. The only advantage to using nitric to dissolve the iron and Pd is you will end up with your Pd separated from the Pt and Rh already. So once you've dissolve all of the iron and Pd you simply cement out the Pd with excess iron. Filter and rinse well to ensure you have no nitric left and then a couple of rinses with 2-3% hcl/h2o will clean up your Pd powder removing any excess iron and you have high purity Pd ready to melt to a bar or sell. The Pt and Rh powder you have left can be separated fairly easily with hot 30% hcl and 30% h202 to dissolve the Pt and this will leave the Rh behind as powder, rinse up well with h20 and it's ready to melt/sell. The Pt you can precipitate from your solution with NaBH4 or iron or aluminum or zinc. Test to make sure it all precipitated and with NaBH4 rinse well with water and dry. With the others rinse with 2-3% hcl/h2o solution to remove any residual iron aluminum or zinc and it's ready for sale.
 
CSM Ian said:
Might want to look into using ammonium hydroxide as a precipitant around pH 3-3.5 range. Only thoughts is some PMG metals might get pulled out due to absorption with large quantities of iron precipitate.
Click to expand...
Best to avoid mixing ammonium hydroxide with any solutions that have nitric in it such as AR. It's a really good way to produce powders that go BOOM!
However you can use NaOH solution but gently take your ph to 3.4 no higher. This will precipitate the iron and avoid precipitating very much of your pms. However the problem with doing so here with the material he is talking about is that the shear volume of iron precipts versus the pgms in solution will drag down a lot of pms with it. And believe me rinsing those iron precipts to get the pms out will be a real pain in the neck and you'll never get it all. Better to cement the pms out with iron rinse well with water and then weak hcl/h20 to remove any excess iron. But yes if you have only a small amount of iron I would absolutely do the ph adjustment and precipitate the iron out. Then selectively precipitate the pms.
 
Yggdrasil said:
Any upsides of using Iron in stead of Copper to cement out the PGMs?
Click to expand...
Anytime you can use iron for cementation instead of copper, go for it. Copper chloride can dissolve finely divided PGM´s, mainly palladium is relatively quick in this behaviour. This make cementations with copper sort of wasteful - you need to bring down the redox of solution by synproportiation reaction of Cu and CuCl2 to form CuCl - which won´t dissolve PGMs anymore.

Plus the "clinging" problem - if some residues of PGM´s are clinging to the surface of iron, it is much easier to remove by simple HCl digestion paired with mild heating.
 

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